Triranjita Srivastava

High-Performance Bimetallic SPR Sensor Based on Periodic-Multilayer-Waveguides

We propose a high-performance bimetallic surface plasmon resonance (SPR) sensor based on periodic-multilayer waveguide and analyze its performance with respect to SPR active metals, such as gold (Au) and aluminum (Al). We found that an ultra thin (~ 3 nm) layer of gold (Au) over aluminum (Al) protects aluminum (Al) from oxidation and exhibits better sensor performance. Using couple-mode theory, we show that the sensitivity and detection accuracy could be appropriately tailored for bimetallic (Au+Al) configuration.

Ultrasensitive Plasmonic Imaging Sensor Based on Graphene and Silicon

We propose an ultrasensitive, accurate, and cost effective surface plasmon resonance sensor based on graphene-on-aluminum and silicon. An angular interrogation method has been theoretically used to study the performance of the sensor in terms of imaging sensitivity, which quantifies the rate of change of slopes of the reflectance curve close to resonance angle. Different optimized design parameters have been reported. It is found that the imaging sensitivity of an aluminum-based sensor is 750% greater than gold, the most widely used SPR active metal. However, graphene-on-aluminum not only prevents the aluminum oxidation but, a monolayer of graphene-on-aluminum exhibits ~400% larger imaging sensitivity compared to that of a conventional gold-film based SPR sensor.

Tamm-plasmon and surface-plasmon hybrid-mode based refractometry in photonic bandgap structures

The transverse magnetic (TM) polarized hybrid modes formed as a consequence of coupling between Tamm plasmon polariton (TM-TPP) mode and surface plasmon polariton (SPP) mode exhibit interesting dispersive features for realizing a highly sensitive and accurate surface plasmon resonance (SPR) sensor. We found that the TM-TPP modes, formed at the interface of distributed Bragg reflector and metal, are strongly dispersive as compared to SPP modes at optical frequencies. This causes an appreciably narrow interaction bandwidth between TM-TPP and SPP modes, which leads to highly accurate sensing. In addition, appropriate tailoring of dispersion characteristics of TM-TPP as well as SPP modes could ensure high sensitivity of a novel SPR platform. By suitably designing the Au/TiO₂/SiO₂-based geometry, we propose a TM-TPP/SPP hybrid-mode sensor and achieve a sensitivity ≥900  nm/RIU with high detection accuracy (≥30  μm⁻¹) for analyte refractive indices varying between 1.330 and 1.345 in 600-700 nm wavelength range. The possibility to achieve desired dispersive behavior in any spectral band makes the sensing configuration an extremely attractive candidate to design sensors depending on the availability of optical sources.

Modeling of a nanoscale rectangular hole in a real metal

We propose and implement a simple and accurate method to analyze a subwavelength rectangular hole in a real metal and obtain the modal characteristics of its fundamental mode. Our results are found to be in excellent agreement with those reported in the literature, obtained by the effective index method (EIM) and finite-element and finite-difference methods. Unlike the EIM, the present method has no ambiguity in its implementation and is able to predict the major field components also, which may be useful in understanding the extraordinary transmission characteristics of such structures.

Propagation characteristics of channel plasmon polaritons supported by a dielectric filled trench in a real metal

We examine the propagation characteristics of channel plasmon polaritons supported by V-grooves and trenches embedded in a real metal. A dielectric filled trench is found to have superior characteristics as compared to a V-groove in terms of mode confinement and propagation length. A substantial decrease in the cutoff depth of the trench due to dielectric has also been observed, making the miniaturized optical components based on such waveguides possible.

On the Performance of Highly Sensitive and Accurate Graphene-on-Aluminum and Silicon-Based SPR Biosensor for Visible and Near Infrared

We demonstrate the numerical analysis of surface plasmon resonance biosensor based on graphene on aluminum and silicon. Employing matrix method, it is found that the proposed sensor exhibits high imaging sensitivity ∼400 RIU−1 to 550 RIU−1 in a large dynamic range from visible to near IR region. It is observed that the application of monolayer or bilayer graphene over aluminum not only protects it from oxidation but also enhances the adsorption of biomolecules, which results in the detection of large refractive indices ranging from aqueous solution to biomolecules (refractive index 1.330 to 1.480) with overall high performance in terms of imaging sensitivity and detection accuracy.

Low index dielectric mediated surface plasmon resonance sensor based on graphene for near infrared measurements

We numerically demonstrate and propose a low index dielectric (Teflon) mediated surface plasmon resonance (SPR) sensor based on graphene in a dielectric?metal?dielectric configuration, for near infrared measurements, by taking advantage of the high adsorption efficiency of graphene and the high-resolution resonance feature of low loss surface plasmons. The proposed configuration supports the low loss surface plasmon mode which is evident from its mode field distribution and effective index dispersion. Results show that at a wavelength of 850?nm, the field intensity enhancement factor at the graphene-sensing layer interface for the proposed chalcogenide Ge20Ga5Sb10S65 (2S2G)?Teflon?Au?graphene based sensor is 20% greater than for the 2S2G?Au?graphene based sensor, thereby increasing the imaging sensitivity by 50%. Moreover, for the proposed sensor, the penetration depth of the field into the sensing region is 340% greater than for the conventional (2S2G?Au?graphene) SPR sensor. The proposed SPR sensor could present new possibilities for SPR imaging and detection for highly sensitive and high-throughput assessment of multiple simultaneous molecular interactions.

Design considerations and propagation characteristics of channel Bragg-plasmon-coupled-waveguides

We present a detailed design principle and propagation characteristics of channel Bragg-plasmon-coupled-waveguide. We have found that there is a significant change in the slope of the phase-velocity dispersion curve leading to an ultranarrow interaction bandwidth (∼765 pm) and group-velocity dispersion (GVD∼±4.5×104 ps/km-nm) that is an appreciably large GVD using a waveguide mode-coupling geometry in any region of the optical spectrum. The effect of waveguide parameters such as channel width, number of bilayers, etc. on a mode-coupling mechanism is also studied with significant emphasis on the propagation loss suffered by the supermodes of the structure. The proposed waveguide exhibits sensitivity as high as 7500 nm/RIU, thereby opening a route for biochemical sensing.

Guided-Mode Analysis of Tamm-Plasmon Polariton at Metal–Heterostructure Dielectric Interface

We present a comprehensive analysis for transverse electric (TE) and transverse magnetic (TM) polarized guided Tamm-plasmon polariton (TPP) mode at metal-heterostructure media interface. We explicitly show that the quarter-wavelength stack condition will not be satisfied for TE or TM polarized TPP mode due to the existence of null-point at metal-heterostructure media boundary. Therefore, we propose an alternate route to design TPP waveguide by solving the mode-dispersion relation for different geometrical parameters in a TiO2/SiO2 bilayer system. The guided TPP-modes (TE and TM) exhibit interesting dispersion characteristics which can be tailored as per the desired application. The group index of TM polarized TPP mode remains constant over a significant wavelength range which results into zero group-velocity dispersion (GVD) at λ ≈ 630 nm wavelength. Also, the propagation length for TM-polarized TPP modes vary between 25 μm to 50 μm in a 630-650 nm wavelength range. However, the variation of GVD for TE-modes exhibit a monotonic variation with an exceptionally large GVD ≈ -3 × 104 ps/km·nm around λ = 632.8 nm.

Comparative study of directional couplers utilizing long-range surface plasmon polaritons

We theoretically investigate the comparative study of coupling characteristics of lateral directional couplers and vertical directional couplers utilizing long-range surface plasmon polaritons (LRSPPs). In particular, the effect of metal stripe thickness, width, the separation between the stripes, and the wavelength of operation, on the characteristics of both types of coupler has been studied in detail. An optimum value of the metal stripe thickness has been observed to obtain the minimum coupling length in both cases. The study should be helpful in designing an efficient directional coupler utilizing LRSPPs.